Prove to be false (5)
I believe the answer is:
rebut
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">prove to be false</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for rebut that I've seen before include "explode" , "Prove the claim wrong" , "Prove to be false or incorrect" , "Contradict or disprove" , "Overturn" .)